We just faced this issue, and found a solution. It's worth a look in your case.

In Contacts, like in Mail, you can have contacts On My Mac or in iCloud. In Contacts > Preferences > General, make sure the Default Account is iCloud.
On the Mac we had trouble with, we had to copy all the contacts from On My Mac to the iCloud account. I did them one alphabet letter at a time, just dragging and dropping. I ended up with a couple of duplicates only, and resolved those by hand.

On my iMac, which has always synced properly, only iCloud is shown in the Accounts section of the sidebar.

See screen shots.

Attachments

accts.jpg (14.3 KiB) Viewed 4236 times

default.jpg (27.31 KiB) Viewed 4236 times

"Design is not just what it looks like and feels like. Design is how it works."
Steve Jobs

Thanks for the hint. I never would have found that preference. I've set iCloud as my default, moved the contacts still in the On My Mac area to iCloud and then deleted every contact in the On My Mac area. All is good.

---
Always burn your bridges. You never know who's coming up from behind.

HI all! This is getting at my problem, but I am still struggling getting my contacts for iCloud and On My Mac to sort out - here's my issue:

I USED to have two "accounts" - one On My Mac and one iCloud, since I added an iCloud account once that became available, so that I could synch across platforms. So everything was working fine - my contacts were available on my iphone and iPad. But, on my laptop, I still had two sections - my iCloud Contacts and my On My Mac Contacts. Unfortunately, the On My Mac contacts folders were named the same as my iCloud folders (since they were essentially a copy from when I added iCloud, but they weren't being updated). I was JUST thinking that I should delete them, when, for some unknown reason, the On My Mac account is no longer parsed out - so now, all of a sudden, I have TWO folders of each group - each with identical names, all in one list in the sidebar, not sorted by account!!! So I don't know which is the iCloud folder/Group or which is the old On My Mac group! Very frustrating! And I don't know why this changed. Some update? (I'm using OS 10.9.5)
So, when I go to preferences, accounts in contacts, it shows iCloud and On My Mac (local) but there is no Account information. And when I go to Preferences, General, there is no option to have a default account (as there used to be) so it seems like the Local Account went away, but not completely.

Should I try to re-add the On My Mac account somehow so that I can sort out the groups? Or is there an easy way to tell which folder is which so I don't delete the most updated group? And actually, how DO you get rid of a group anyway? I don't seem to be able to delete a group from my sidebar.

Any thoughts or help would be appreciated! Thanks! I maintain some large email distribution groups for the Port Angeles Christmas Count so I really don't want to start over, if possible! Thanks!